Among the tricyclic compounds which can be prepared by the process of the invention, two of them, more precisely 7,7-dimethyl-6-methylene-tricyclo[6.2.1.0.sup.1,5 ] undecan-2-one and 7,7-dimethyl-6-methylene-tricyclo [6.2.1.0.sup.1,5 ] undec-2-ylmethyl alcohol, are naturally occurring compounds. Both were in fact isolated from vetiver oil by means of an extremely complex and expensive process [see "The Flavour Industry" 1, 623 (1970) and Perfume & Essential Oil Records 60, 307 (1963)]. The said process essentially consists in submitting the essential oil to several fractional distillations and numerous separations effected by means of column chromatography. It has also to be pointed out that said compounds are relatively minor constituents of the said essential oil, this latter containing in fact a proportion of 0.1 to 0.5% (parts by weight) of each compound.
We have now found that pure 7,7-dimethyl-6-methylene-tricyclo[6.7.1.0.sup.1,5 ] undecan-2-one possess a very distinct and powerful odour presenting an original woody character. Moreover, this latter is very stable and easily reproducible whereas the odour of the natural essential oil, which results from the over all effect of the odours of the individual constituents of the said oil, can vary depending on the origin and the purity of the said natural essential oil.
Owing to its particular olfactive properties the above mentioned tricyclic ketone can be widely used in the art of perfumery. Its use is broader than that of vetiver oil itself and it enables the perfumer to create totally original woody notes. Furthermore, the said ketone possesses a very appreciated reinforcing and fixative effect.
One of the processes of the invention consists in preparing the above mentioned tricyclic ketone by using a relatively cheap starting material. Said starting material is known in the art as vetivenic or zizanoic acid (7,7-dimethyl-6-methylene-tricyclo[6.2.1.0.sup.1,5 ] undec-2-yl carboxylic acid). This compound may be obtained in large amounts and at a low price, as a by-product resulting from the purification of vetiver essential oil.
By means of a novel process of synthesis, industrially and economically more advantageous than the isolation of the said tricyclic ketone from the natural vetiver oil, it is now possible to place at the disposal of perfumers and flavourists a pure 7,7-dimethyl-6-methylene-tricyclo[6.2.1.0.sup.1,5 ] undecan-2-one. The difficulties of supply, storage and purification of the natural essential oil are thus avoided.
7,7-dimethyl-6-methylene-tricyclo[6.2.1.0.sup.1,5 ] undec-2-ylmethyl alcohol may be easily obtained from zizanoic acid, by reducing this latter compound by means of an alkali metal aluminiumhydride.
The discovery of the interesting organoleptic properties of 7,7-dimethyl-6-methylene-tricyclo[6.2.1.0.sup.1,5 ] undecan-2-one in particular has thus encouraged the man in the art to further explore a whole series of analogous tricyclic derivatives which represent a new class of valuable perfuming and flavouring ingredients.